1. Field of Invention
The present invention relates generally to automatic transmissions and, more specifically, to a system and method for fast fill of an accumulator for an automatic transmission.
2. Description of the Related Art
Conventional vehicles known in the art typically include an engine having a rotational output as a rotational input into a transmission such as an automatic transmission. The engine generates the rotational output which is selectively translated to the transmission which, in turn, translates rotational torque to one or more wheels. The transmission changes the rotational speed and torque generated by the engine through a series of predetermined gearsets, whereby changing between the gearsets enables a vehicle to travel at different vehicle speeds for a given engine speed.
In addition to changing between the gear sets, the automatic transmission is also used to modulate engagement with the rotational output of the engine, whereby the transmission can selectively control engagement with the rotational output of the engine so as to facilitate vehicle operation. By way of example, torque translation between the rotational output of the engine and the input into the automatic transmission is typically interrupted while the vehicle is parked or idling, or when the transmission changes between the gearsets. In conventional automatic transmissions, modulation is achieved via a hydrodynamic device such as a hydraulic torque converter. However, modern automatic transmissions may replace the torque converter with one or more electronically and/or hydraulically actuated clutches (sometimes referred to in the art as a “dual clutch” automatic transmission). Automatic transmissions are typically controlled using hydraulic fluid and a hydraulic system including a pump assembly, a valve body having one or more solenoid valves, and an electronic controller. The pump assembly provides a source of fluid power to the solenoid valves of the valve body which, in turn, are actuated by the controller so as to selectively direct hydraulic fluid throughout the automatic transmission to control modulation of rotational torque generated by the rotational output of the engine. The solenoid valves are also typically used to change between the gear sets of the automatic transmission, and may also be used to control hydraulic fluid used to cool and/or lubricate various components of the transmission in operation.
It is known to provide a hydraulic accumulator to store hydraulic fluid for the hydraulic system used in the automatic transmission. Generally, the hydraulic accumulator fluidly communicates with the valve body of the hydraulic system of the automatic transmission. Typically, the pump assembly is turned on to provide enough hydraulic fluid and pressure to meet the needs of the automatic transmission, for example, providing enough hydraulic fluid to clutches of the automatic transmission. However, this approach is more expensive and results in more power consumption to fill the hydraulic accumulator.
In addition, the hydraulic accumulator must be coordinated with an engine restart event. A launch clutch of the automatic transmission must be filled before the engine produces output torque. This approach to refilling the hydraulic accumulator means that after an engine restart event, it may take several seconds to refill the hydraulic accumulator to allow for the next engine stop event. This is not desirable to a vehicle driver who may be in a slow traffic jam or at a drive-through line.
Accordingly, it is desirable to assist an automatic transmission in stop/start vehicle applications by actively filling and controlling a discharge of the accumulator when commanded. It is also desirable to provide a control strategy or method to allow for near instantaneous refill of the hydraulic accumulator under specific conditions. Thus, there is a need in the art to provide a system and method for fast fill of the hydraulic accumulator for an automatic transmission.